Fusarium moniliforme is one of the predominant fungi associated with corn intended for human and animal consumption world-wide. Fumonisins, food-borne carcinogens that occur naturally in corn, were first isolated and chemically characterized in South Africa in 1988. The major metabolite, fumonisin B1 (FB1), was subsequently shown to cause leukoencephalomalacia (LEM) in horses, pulmonary edema syndrome (PES) in pigs, and liver cancer in rats. FB1 is also a cancer promoter and initiator in rat liver; hepatotoxic to horses, pigs, rats, and vervet monkeys; cytotoxic to mammalian cell cultures; and phytotoxic to several plants. Fumonisins in home-grown corn have been associated with an elevated risk for human esophageal cancer in Transkei and China. There is a close structural similarity between fumonisin and sphingosine, and fumonisins are the first known naturally occurring inhibitors of sphingolipid biosynthesis. The natural occurrence of FB1, together with FB2 and FB3, has been reported in commercial corn and/or corn-based feeds and foods from Argentina, Australia, Brazil, Botswana, Bulgaria, Canada, China, Egypt, France, Italy, Japan, Kenya, Hungary, Nepal, Peru, South Africa, Switzerland, United States, and Zimbabwe. It is imperative that safe levels of fumonisins in human foods and animal feeds should be determined and realistic tolerance levels established as soon as possible.